System and method for performance optimization and through a distributed antenna system

ABSTRACT

A method for operating a Distributed Antenna System (DAS) includes providing a plurality of Digital Remote Units (DRUs), each configured to send and receive wireless radio signals and providing a plurality of inter-connected Digital Access Units (DAUs), each configured to communicate with at least one of the plurality of DRUs via optical signals and each being coupled to at least one sector of a base station. The method also includes providing a plurality of sensors operable to detect activity at each of the plurality of DRUs, turning off a DRU downlink signal at one of the plurality of DRUs in response to an output from one of the plurality of sensors, and turning on a DRU downlink signal at another of the plurality of DRUs in response to an output from another of the plurality of sensors.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/621,192, filed Feb. 12, 2015, which claims priority to U.S.Provisional Patent Application No. 61/939,050, filed on Feb. 13, 2014,entitled “System and Method for Performance Optimization In and Througha Distributed Antenna System,” the disclosures of which are herebyincorporated by reference in their entirety for all purposes.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to communication networks.More particularly, embodiment of the present invention provide methodsand systems related to the provision and operation of distributedantenna systems (DAS). Merely by way of example, the present inventionhas been applied to distributed antenna systems. Another example of thepresent invention could include a system of distributed and configurableradios connected via a router to donors feeding a Base Station. Themethods and systems described herein are applicable to a variety ofcommunications systems including systems utilizing variouscommunications standards.

According to an embodiment of the present invention, a method foroperating a Distributed Antenna System (DAS) is provided. The methodincludes providing a set of Digital Remote Units (DRUs) operable to sendand receive wireless radio signals Each of the set of DRUs is associatedwith a geographic area. The method also includes providing a DigitalAccess Unit (DALI) operable to communicate with the set of DRUs via anoptical signal The DAU is coupled to at least sector of a basetransceiver station (BTS), The method further includes receiving uplinksignals at one or more of the set of DRUs and Ill onitoring trainactivity in the geographic areas associated with the set of DRUs Themethod includes increasing a gain coefficient associated with one of theset of DRUs in response to determining an increase in monitored trainactivity in the geographic area associated with the one of the set ofDRUs, decreasing a gain coefficient associated with another of the setof DRUs in response to determining a decrease in monitored trainactivity in the geographic area associated with the another of the setof DRUs, and transmitting, to the DAU, scaled uplink signals associatedwith the one of the set of DRUs and the another of the set of DRUs

According to another embodiment of the present invention, a system foroperating a Distributed Antenna System (DAS) is provided. The systemincludes a plurality of Digital. Remote Units (DRUs), each configured toreceive wireless radio uplink signals and transmit wireless radiodownlink signals and a plurality of inter-connected Digital Access Units(DAUs), each configured to communicate with at least one of theplurality of DRUB via optical signals and each being coupled to at leastone sector of a base station. The system also includes a plurality ofdetectors, each configured to measure uplink power at one of theplurality of DRUs and a processor coupled to the plurality of detectorsand configured to vary gain coefficients for each of the wireless radiouplink signals in response to the measured uplink power.

According to a specific embodiment of the present invention, a methodfor operating a Distributed Antenna System (DAS) is provided. The methodincludes providing a plurality of Digital Remote Units (DRUs), eachconfigured to send and receive wireless radio signals and providing aplurality of inter-connected Digital Access Units (DAUs), eachconfigured to communicate with at least one of the plurality of DRUs viaoptical signals and each being coupled to at least One sector of a basestation. The method also includes providing a plurality of sensorsoperable to detect activity at each of the plurality of DRUs and turningoff a DRU downlink signal at one of the plurality of DRUs in response toan output from one of the plurality of sensors. The method furtherincludes turning on a DRU downlink signal at another of the plurality(DRUs) in response to an output from another of the plurality ofsensors.

Embodiments of the present invention relate to a dynamic configurationof the DAS network's digital remote units (DRUs) parameters , such thatthe DRU's parameters can he modified, despite a fixed physicalarchitecture. An example of a digital remote units (DRU) is aconfigurable radio with integrated routing capability located at aremote location from the base station (BTS) or baseband units (BBU). Anexample of a digital access unit (DAU) is a configurable radio withintegrated routing capability co-located with the base stations orBaseband Units. This objective may be accomplished, for example, byusing a plurality of digital remote units (DRUs) based on a DistributedAntenna System (DAS). Each DAS may receive resources (e.g., RE carriers,Long Term Evolution Resource Blocks, Code Division Multiple Access codesor Time Division Multiple Access time slots) from a central base stationincluding a plurality of sectors and distribute the resources to aplurality of digital remote units (DRUs). Each DRU can serve as anantenna, receiving and transmitting signals, and thereby providingnetwork coverage to a local geographic area surrounding the physicalDRU. The DAS may be physically coupled to the base station and to theplurality of DRUs, e.g., through an optical fiber link. Thus, resourcesprovided by one base station may be distributed to a plurality of DRUs,thereby providing coverage over a larger geographical area.

A DAS may be coupled (e.g., through another optical fiber link) to oneor more other BTSs. Therefore, the DAS may also: (1) allocate part ofthe resources associated with another base station (which may bereferred to as a sector) to the DRUs physically coupled to the DAS:and/or (2) allocate resources from the sector physically coupled to theDAS to serve DRUs physically coupled to another DAS. This may allow asystem to dynamically allocate resources from a plurality of sectors toa network of DRUs (e g , responding to geographic and temporal patternsin device usage), thereby improving the efficiency of the system andmeeting desired. capacity and throughput objectives and/or wirelesssubscriber needs.

A DAS network performance can be optimized for environments that haveintermittent activity, as example along a train track Train activity ateach DRU can be synchronized with the plurality of DRU parameters inorder w improve performance and reduce operational expenses. Althoughsome embodiments of the present invention are illustrated in the contextof train applications, the present invention is not limited to thisparticular transportation system and other transportation systems,including highways, roads, rivers, and the like are included within thescope of the present invention. Therefore, although trains are oneexample of a system with which embodiments of the present invention canbe utilized, other vehicles including cars, trucks, boats, planes, andthe like can benefit from embodiments of the present invention. One ofordinary skill in the. art would recognize many variations,modifications, and alternatives

According to an embodiment of the present invention, a system foroptimizing performance in a Distributed Antenna System is provided. Thesystem includes a plurality of Digital Remote Units (DRUs) configured tosend and receive wireless radio signals and a plurality ofinter-connected Digital Access Units (DAUS), each configured tocommunicate with at least one of the plurality of DRUs via opticalsignals, and each being coupled to at least one sector. The system alsoincludes a plurality of detectors to measure uplink power at each of theplurality of DRUs and an algorithm operable to turn off or on DRU uplinksignals from one or more of the plurality of DRUs based ori the uplinkpower detected by the plurality of detectors.

Each of the plurality of detectors can be implemented digitally usingsignal processing or as a discrete analog device. Each of the pluralityof DAUB can be configured to communicate with the at least one of theDRUs by sending and receiving signals over at least one of an opticalfiber, an Ethernet cable, microwave line of sight link, wireless link,or satellite link. The DRUs can be connected in a loop to a plurality ofDAUB.

According to another embodiment of the present invention, a system foroptimizing performance in a Distributed Antenna System is provided. Thesystem includes a plurality of Digital Remote Units (DRUs) configured tosend and receive wireless radio signals and a plurality ofinter-connected Digital Access Units (DAUS), each configured tocommunicate with at least one of the DRUs via optical signals, and eachbeing coupled to at. least one sector, The system also includes aplurality of sensors operable to detect activity at each of theplurality of DRUs and an algorithm to turn off and on ORE downlinksignals and DRU uplink signals associated with each of the plurality ofDRUs based, at least in part, on outputs of the plurality of sensor.

In an embodiment, each of the plurality of DAUs is configured tocommunicate with the at least one of the DRUs by sending and receivingsignals over at least one of an optical fiber, an Ethernet cable,microwave line of sight link, wireless link, or satellite link. Each ofthe DAUs can be co-located with the at least one sector. Each of theplurality of DAUs can be connected to a plurality of DRUs, for example,with at least some of the plurality of DRUs being connected in a daisychain configuration or with the plurality of DRUs being connected to atleast one of the plurality of DAUs in a star configuration.

According to a specific embodiment of the present invention, anon-transitory computer-readable storage medium comprising a pluralityof computer-readable instructions tangibly embodied on thecomputer-readable storage medium, which, when executed by one or moredata processors, provide routing of wireless network signals, isprovided. The plurality of instructions include instructions that causethe data processor to decode a digital signal and instructions thatcause the data processor to identify a Digital Remote Unit (DRU) basedon the decoded signal The plurality of instructions also includeinstructions that cause the data processor to convert the digital signalinto a radio-frequency signal, instructions Chat cause the dataprocessor to dynamically determine an assignment pairing the DRU withone or more Base Transceiver Station sectors, the assignment being atleast partly determined by dynamic geographic discrepancies in networkuse, and instructions that cause the data processor to transmit thedigital signal to the one or more assigned sectors.

Numerous benefits are achieved by way of the present invention overconventional techniques. For instance, embodiments of the presentinvention allow a network to effectively respond to a geographicallychanging mobile user base. For example, users concentrated in a traintraverse the network of DRUs along the train track, some DRU resourcesmay be allocated to serve this train only for time periods when theusers actually are or are predicted to be at this location. Thus, anetwork operator need not either waste DRIII resources to providecoverage in other sections of the track during these times, nor must itdegrade system performance by adding noise from non-active DRUs. Rather,DRU resources may be flexibly managed and controlled, thereby improvinga network's efficiency, usage, overall performance and economics.Further, due to this foreseeable efficiency, specialized applicationsand enhancements may be enabled, such as flexible simulcast, automatictraffic load-balancing, network and radio resource optimization, networkcalibration, autonomous/assisted commissioning, carrier pooling,automatic frequency selection, radio frequency carrier placement,traffic monitoring, traffic tagging, traffic shaping, trafficallocation, traffic management and the like. Embodiments may also beimplemented to serve multiple operators, multiple standards, multi-moderadios (modulation-independent) and multiple frequency bands peroperator to increase the efficiency and traffic capacity of theoperators' wireless networks.

These and other embodiments of the invention along with many of itsadvantages an features are described in more derail in conjunction withthe text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high level schematic diagram illustrating a wireless networksystem providing coverage to a geographical area according to anembodiment of the present invention;

FIG. 2 is a high level schematic diagram illustrating a wireless networksystem comprising interconnected DMA, the network providing coverage toa geographical area according to an embodiment of the present invention;

FIG. 3 is a high level schematic diagram illustrating a wireless networksystem comprising interconnected DAUs and multiple base station hotels,the network providing coverage to a geographical area according to anembodiment of the present invention;

FIG. 4 is a high level schematic diagram illustrating a distributedantenna system (DAS) that covers a portion of a train track according toan embodiment of the present invention;

FIG. 5 is a high level flowchart illustrating a method of detectingtrain activity and controlling DRU Up-Link signals according to anembodiment of the present invention;

FIG. 6 is a high level flowchart illustrating a method of detectingtrain activity and activating and de-activating DRU downlinktransmitters, according to an embodiment of the present invention;

FIG. 7 is a high level schematic diagram illustrating a DAU according toan embodiment of the present invention;

FIG. 8 is a high level schematic diagram illustrating a DRU according toan embodiment of the present invention;

FIG. 9 is a high level schematic diagram illustrating a computer systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Wireless and mobile network operators face the continuing challenge ofbuilding networks that effectively manage high data-traffic growth ratesand fluctuating traffic distribution. To ensure customer satisfaction,network operators attempt to provide networks that are available andFunctional in most locations where their clients will expect to be ableto use their devices. This is a difficult task, as it is bard todetermine how to geographically allocate resources, given theunpredictable nature of where and how users will wish to use theirdevices.

Allocating network resources is complicated by users mobility andunpredictability. For example, configuring a network to effectivelyallocate wireless network resources to users on a train may presentchallenges (e.g., with regard to available wireless capacity and datathroughput) as the train travels along the track.

Network operators are tasked with establishing wireless (e.g., cellularmobile communication systems) coverage across one or more largegeographic areas. As described in greater detail below, dividing ageographic area into a plurality of cells allows a network operator toreuse resources (e.g., spectrum) across geographically separated cells.,

FIG. 1 is a diagram illustrating one wireless network system 100 thatmay provide coverage to a. geographical area according to an embodimentof the present invention. The geographic area in FIG. 1 is along traintrack 120. Although embodiments have been described with reference to atrain track example, it will be evident that various modifications andchanges may be made to these embodiments without departing from thebroader spirit and scope of the invention. System 100 may include adistributed antenna system (DAS), which may efficiently use base-stationresources. One or more base stations 105 (also referred to as basetransceiver stations (BTS)) may be located in a central location and/orat a base station hotel. One or more base stations 105 may include aplurality of independent outputs or radio resources, known as sectors110. Each sector 110 may be responsible for providing wireless resources(e.g., RF carrier signals, Long Term Evolution Resource Blocks, CodeDivision Multiple Access codes, Time Division Multiple Access timeslots, etc.). The resources may include one or more resources that allowa wireless user mobile device to effectively and wirelessly send andreceive communications over a network. Thus, the resources may includeone or more resources, such as those listed above, that allow a signalto be encoded or decoded in a manner to prevent the signal frominterfering with or being interfered with by other wireless signals.

Each sector may be coupled to a digital access unit (DAU) 115, which mayinterface sector 110 (and thus base station 105) with digital remoteunits (DRUs) installed along train track 120. The coupling may representa physical coupling, For example, DAU 115 may be connected to sector 110and/or DRU 1 via a cable, a link, fiber, an RE cable, an optical fiber,an Ethernet cable, microwave link with or without line of sight,wireless link, satellite link, etc. In some instances, DAU 115 isconnected to sector 110 via an RE cable. In some instances, DAU 115 isconnected to one or more DRU s via an optical fiber or Ethernet cable.An associated sector 110 and DAU 115 unify be located near each other orat a same location DAU 115 may convert one or more signals, such asoptical signals, RF signals, digital signals, etc. DAU 115 may include amulti-directional signal converter, such that, e.g., RE signals may beconverted to optical signals and optical signals to RF signals, or toconvert signals between a signal type associated with a sector and asignal type associated with a DRU. In one embodiment, DAU 115 converts asector's downlink RE signals to optical signals, and/or converts a DRU'suplink optical signals to RE signals. DAU 115 may also or alternativelycontrol routing of data and/or signals between sectors and DRUs, asexplained in greater detail below. DAU 115 may generate, collect and/orstore traffic statistics, such as a number of communications, calls,network-access and/or communication sessions, traffic volumes, qualityof service data etc between sector 110 and one or more DRUs.

Each DAU 115 may be coupled to a plurality of digital remote units(DRU). The plurality of DRUs may be coupled to the 115 through, e.g., adaisy-chain or loop (indirectly coupling a DAU with one or more DRUs)and/or star configuration (directly coupling a DAU to multiple DRUs).FIG. 1 shows an example of daisy-chain configurations, wherein a DAUcouples to a first DRU directly (e.g., direct connection from DAU 1 toDRU 1), a second DRU indirectly (e.g., indirect connection from DAU 1 toDRU 2 through DRU 1), a third DRU indirectly (e.g., indirect connectionfrom DAU 1 to DRU 3 through DRUs 1 and 2), etc. FIG. 1 also shows anexample of star configurations, wherein a DAU couples to multiple DRUsdirectly (e.g., direct connections from DAU 1 to DRU 1 and DRU 15).

Each of the DRUs can provide coverage and capacity within a geographicalarea.

physically surrounding the DRU. DRUs may be strategically located toefficiently provide combined coverage across a larger geographical area.For example, DRUs 1 may be located e.g,, along a train track., and/orcoverage areas associated with adjacent DRUB may be barely overlapping.A network may include a plurality of independent cells that span a totalcoverage area.

As illustrated in FIG. 1. DRU 8 through DRU 14 are daisy chained to eachother, with DRU 8 coupled, via an optical fiber, to DAU 1 (115). Becauseof the daisy chain architecture of this embodiment, as the train movesalong the track from the cell associated with DRU 14 toward the cellassociated with DRU 8, the uplink signals communicated through DRU 14are transported down the daisy chain toward DRU 8. In someimplementations, the noise associated. with the uplink signals from eachof the DRUs in the daisy chain is added as the uplink signals from thevarious DRUs are combined as the uplink signals move down the daisychain toward DRU 8. As a result, for an uplink signal received at DRU14, the noise from each of the intervening DRUs (DRU 13 through DRU 8)is combined to the original signal, reducing the signal to noise ratioas the uplink signal moves down the daisy chain.

As described herein, in order to improve, the signal to noise ratio ofthe uplink signals, the DRUs not in active communication with the trainaxe deemphasized in various embodiments. As an example, theamplitudelpower of signals and noise associated with DRUs not in activecommunication with the train can he decreased when the level ofcommunication with the train is low and increased for the DRUs in thevicinity of the train, Additional description related to decreasing thenoise signal through control of the uplink signals is provided, forexample, in relation to FIG. 4 below. In addition to control of theuplink signals, DRUs can be controlled to decrease the power associatedwith downlink signals broadcast by DRUs that are not in activecommunication with a train. Accordingly, power budgets and operationalexpenses can be reduced Lw control of the uplink and downlink traffic inareas where no train traffic is present. One of ordinary skill in theart would recognize many variations, modifications, and alternatives.

In conventional DAS networks, a first set of remote units in a firstgeographic area can be connected to a first BTS or a first sector of aBTS and a second set of remote units in a second geographic area can beconnected to a second BTS or a second sector of the BTS. In anenvironment in which people are communicating while a train is moving,the calls for the users will be handed off from the first BTS to thesecond BTS as the train moves from the first geographic area to thesecond geographic area, If the volume of users is large, the heavymessaging traffic at the point of the hand offs can result in droppedcalls, decreased data rates, and the like. Embodiments of the presentinvention provide methods and systems to ameliorate these problemsassociated with conventional systems.

Referring to FIG. 1, a benefit provided by the illustrated DAS network,with DRUs associated with a single sector of the BTS positioned alongthe track (e.g., DRU 1 through DRU 7 can be connected to Sector 1(110)), is that as the train moves along, the track from Cell 1 to Cell7, no handoffs are needed, reducing the number of dropped calls andinterruptions in data service. The digital DAS system illustrated inFIG. 1 provides DRUs positioned along, the track in a generally linearmanner in contrast with closed cell structures in which the cells arepacked together in a hexagonal pattern covering a generally hexagonalcircular coverage area.

It should be noted that although a single train moving along the tracksis discussed in some embodiments, it will be appreciated that multipletrains can be traveling along the tracks concurrently and thediscussions related to a single train can he extended to multiple trainsas appropriate to the particular application.

Each cell may he assigned to a sector 210. FIG. 2, for example, shows anembodiment in which Sector 1 provides resources to Cells 15 to 21,Sector 2 to Cells 1 to 7, and Sector 3 to Cells 8 to 14. An associatedsector may provide each DRU with resources, such as RF carriers,resource blocks, etc. In one embodiment, each of a plurality of sectors210 is associated with a set of “channels” or frequency ranges. The setof channels associated with each sector 210 may be different from a setof channels associated with other sectors 2 and 3 in base station 205. Anetwork may be configured such that neighboring cells are associatedwith different channels (e.g., by being associated with differentsectors 210), as shown in FIG. 2. This may allow channels to be reusedacross multiple cells without the risk of creating interference.

In the embodiment shown in FIG. 1, each sector 110 is connected to anassociated subset of all of the DRUs in the network. Thus, for example,Sector 1's resources (e.g., assigned channels) cannot be used by a DRUlocated in Cell 8 without a physical alteration to the network hardware(e.g., by re-routing an optical Fiber). This limitation is avoided bythe embodiment shown in FIG. 2. Specifically, DMA may be dynamicallyassigned to sectors 210 based on an interconnection between DAUs 215.Thus, for example,. DRUs 8-14 in Cell 8 to 14 may initially all beassigned to Sector 3. (FIG. 2.) Subsequently, DRU 7 may be assigned toSector 3 and DRU 14 max be assigned to Sector 1. In such instances,signals to DRU 7 may pass from Sector 2 through DRU 2 and through DAU 3.Similarly, signals may pass from. DRU 14 through DAUs 3 and DSU 1 toSector 1. In this manner, a sector may he indirectly connected with alarger subset of DRUs in a network or with all DRUs in a network.Communications between DAUs may be partly controlled by one or moreservers 225, as explained in greater detail below.

DAUs 210 may be physically and/or virtually connected. For example, inone embodiment, DAUs 210 are connected via a cable or fiber (e.g., anoptical fiber, an Ethernet cable, microwave link with or without line ofsight, wireless link, or satellite link). In one embodiment, a pluralityof DAUs 210 are connected to a wireless network, which allowsinformation to be transmitted from one DAU 210 to another DAU 210 and/orallows information to be transmitted from/to a plurality of DAUs 210.

As shown in FIG. 3, a multi-operator system or a system with multiplebase stations of one operator or a combination of both may includemultiple base stations (or multiple base station hotels) 305. A NeutralHost scenario is defined when multiple operators co-exist on the sameinfrastructure and a the system is hosted by either one of the operatorsor a 3^(rd) party. Different base stations 305 may be associated withthe same, overlapping, non-overlapping or different frequency bands.Base stations 305 may he interconnected, to serve a geographic area. Theinterconnection may include a direct connection extending between thebase stations (e.g., a cable) or an indirect. connection (e.g. each basestation connecting to a DAU, the DAUs being directly connected to eachother). The greater number of base stations may increase the ability toadd capacity for a given cell. Base stations 305 may represent:independent wireless network operators and/or multiple standards (WCDMA,LTE, etc.), and/or they may represent provision of additional RFcarriers as well as additional baseband capacity. In some embodiments,base station signals are combined before they are connected to a DAU, asmay be the case for a Neutral Host application. In one instance, asshown in FIG. 3. sectors from BTS 1 are directly coupled to the sameDAUs and/or DRUs that are directly coupled to sectors to BTS N. In someother instances, one or more sectors from different BTS may be directlycoupled to DAUs not shared by sectors of one or more other DAUs.

FIG. 4 is a diagram illustrating a distributed antenna system (DAS) thatcovers a portion of a train track according to an embodiment of thepresent invention. As illustrated in FIG. 4, this high level schematicdiagram illustrates a wireless network system comprising daisy chainedDRUs with the Up -Link signals from each DRU being scaled and summed,with the network providing coverage to a geographic area. In thisexample, DRU 15 to DRU 21 covering cells 15 to 21 are assigned to Sector1. Based on network hardware and architecture, signals from DRUs 15-21are routed to DAU 1. DAU 1 combines the uplink signals from DRU 15-21 orreceives signals that are combined, in turn, at each of the DRUs. Inthis embodiment, DAU 1 associates gain coefficients cam {α, β, . . . ,δ} for each of the respective DRUs {15, 16 . . . 21} assigned to DAU 1.The gain coefficients are used to scale the unlink signals. The equationbelow demonstrates how the uplink signals from DRUs k through N (e.g.,15-21) are combined to provide scaled uplink signals that aretransmitted to DAU 1.

${\sum\limits_{{DRU}_{k}}^{N}{DRU}} = {{\alpha \cdot {DRU}_{k}} + {\beta \cdot {DRU}_{k + 1}} + {\ldots\mspace{14mu}{\delta \cdot {DRU}_{N}}}}$

The gain coefficients are adjustable from zero to one, providing forindividual control over the signals uplinked using each DRU. In someembodiments, the sum of the scaled uplink signals from the DRUs can bereferred to as a scaled uplink signal, which is received at the DAU. Inaddition to uplink control, downlink control is provided in someembodiments. As an example, as a train moves from Cell 15 towards Cell21, initially Cell 15 is at full power (i.e., α 1) and Cell 21 is off(δ=0). Cells between Cell 15 and Cell 21 are at levels between zero andone. As the train moves towards Cell 21. the gain coefficients areadjusted by decreasing a and increasing δ to match the gain associatedwith the DRUs to the position of the moving train.

A train contains a high density of mobile users. As this group of mobileusers travel along the track different DRUs are active. However, the UpLink signal presented to BTS 405 comprises the addition of all the DRUsconnected to DAA I. Even if a DRU experiences no activity it willcontribute to the overall noise floor when all gain coefficients are setto unity. The DAS system in FIG. 4 can alter the gain coefficientsthereby turning the Uplink channels from the DRUs up or down for on oroff) depending on the train activity at their respective sites, DRUswith no activity can be switched off in order to reduce the noisecontribution associated with those inactive DRUs. As discussed above, inaddition to control of the uplink channels, control of downlink channelscan be implemented to reduce the power consumption of DRUs that are notin active communication with the train and the resulting operatingexpenses.

FIG. 5 is a simplified flowchart illustrating a method of controllingDRU uplink gain according to an embodiment of the present invention. Inthis embodiment, a performance optimization algorithm for the DASnetwork alongside of the train track is provided. In functional block505, the DRUs are assigned to various DAUs. As an example. DRUsconnected to a DAU using an optical fiber can be assigned to the DAU towhich they are connected. The DAUs are connected to sectors in the BaseTransceiver Stations (BTSs). Functional block 510 assigns a subset ofthe DRUs to a section of the train track. This assignment relates thegeographic location of the cells associated with the DRUs to theirlocations along the track. The network of DRUs, DAUs and BTSs areconfigured and the assignments are stored in memory (515).

10451 The downlink signals from the BTS sectors are routed to theassigned DATA and subsequently DRUs (520). The DRU uplink signalsreceived at the DRUs are routed to the assigned DAU for the subset ofDRUs assigned to the DAU. The uplink signals from the DRUs are scaled bya gain coefficient and then combined and fed to the sector for thatspecific BTS, in functional block 525. As described above, inactive DRUscan contribute noise to the uplink signals thereby degrading the overallsystem performance. Functional block 530 monitors the train activity ateach respective DRU, referred to as DRU_(k). Although embodiments havebeen described with reference to a train activity monitor example, itwill be evident that various modifications and changes may be made tothese embodiments without departing from the broader spirit and scope ofthe invention.

The train activity monitor can be a sensor (e.g., an external monitor)that detects motion of the train along the track or it could be ameasurement of the cellular signal strength or the cellular dataactivity in a geographic area A monitor can be implemented using signalprocessing inside the DRU, for example, based on the uplink signalstrength. An external monitor could be an optical detector, vibrationdetector, radar detector, etc. In some embodiments, train schedules areutilized to provide inputs to the system, effectively providingmonitoring inputs. In other embodiments, communication from the train(e.g., a broadcasted GPS location) can be utilized as a monitor input,in place of or in conjunction with other monitors. One of ordinary skillin the art would recognize many variations, modifications, andalternatives.

The train activity monitor will become active when a train traverses aDRU cell that provides coverage to a geographical area. This will he anindication that the DRU will momentarily experience a large number ofmobile users as the train enters the geographic area associated with theDRU. in some embodiments, a threshold will be set for the train activitymonitor.. Although embodiments have been described with reference to athreshold trigger example, it will he evident that various modificationsand changes may he made to these embodiments without departing from thebroader spirit and scope of the invention.

If the train activity monitor indicates that the activity is increasing(or goes above a threshold setting), then the gain coefficientcorresponding to that DRU will be transitioned toward unity (540). Thiswill effectively connect the DRU with the given BIS sector, via the DAU.If the train activity monitor indicates that the activity is decreasing(or falls below the threshold) then the DRU uplink gain coefficientcorresponding to that DRU will be transitioned toward zero (550). Thiswill reduce the noise contribution from those DRUs that have no activemobile users passing through their cells.

A closed loop is demonstrated in the flowchart 500, whereby the trainactivity monitors are continually or regularly analyzed or compared tothe threshold and the gain coefficients are adjusted accordingly, insome embodiments, the closed loop returns to block 530 after decisionpoint 535 and the gain adjustments in blocks 540 or 550.

The train activity monitor sensors are thus configured to provide datathat is utilized by the system to control the operation of the DRUs asdescribed herein. As illustrated by the operation discussed in relationto FIG. 5, some embodiments increase/decrease the gain coefficients insmall steps or continuously to vary the gain between values of zero andone. As an example, as a train approaches a DRU, the gain can he turnedup gradually, peaking at one when the train is adjacent, to the DRU andthen gradually turning the gain down as the train leaves the area of theDRU. Thus, some embodiments utilize a scale that increases/decreases thegain in response to increases/decreases in train activity In otherembodiments, the train activity is compared to a threshold. If thethreshold is exceeded, the DRU uplink gain is set to unity. If theactivity does not exceed the threshold, the DRU uplink gain is set tozero. One of ordinary skill in the art would recognize many variations,modifications, and alternatives.

FIG. 6 is a flowchart of one embodiment of the performance optimizationalgorithm for the DAS network alongside of the train track. Flowchart600 has a similar functionality to flowchart 500, with the exceptionthat the DRU transmitters and or receivers will be controlled (e.g.,turned off and on) depending on the train activity monitor. The primaryobjective of turning off the DRU transmitters and or receivers is toreduce the operational expenses and reduce the interference to MacroBTSs in neighboring cells. In some embodiments, the DRU downlink path isnot turned off, but decreased in power as a function of the trainactivity that is monitored. In these embodiments, the train activity ismonitored (630) on a periodic or other temporal basis. If the trainactivity is increasing, then the power associated with the downlinktransmitter is increased toward a maximum power (similar to block 640).If the train activity is decreasing, then the power associated with thedownlink transmitter is decreased toward zero (similar to block 650).Thus, blocks 540 and 550 illustrated in FIG. 5 can be substituted forblocks 640 and 650 in FIG. 6. Likewise. blocks 640 and 650 illustratedit FIG. 6 can be substituted for blocks 540 and 550 in FIG. 5 asdiscussed above.

FIG. 7 illustrates components of a DAU 700 according to an embodiment ofthe invention. DAU 700 may include a router (i.e., Local Router 705).DAU 700 may include one or more ports 715 and 720. Ports 715 and 720may, es,, enable DAU to connect to the Internet. and/or a Host Unit or aserver 725. Server 725 may at least partly configure the DAU and/orcontrol the routing of the signals between various Local Router ports.Server 725 may be, e.g., at least partly controlled by a remoteoperational control 730 (e.g., to set re-assignment conditions, identifyassignments, store assignments, input network configurations,receive/collect/analyze network usage, etc

DAU 700 may include one or more physical nodes 710, which may be coupledto Local Router 705 by one or more first-end ports 735. Each physicalnode 710 may include one, two ,or more ports, such as first-end ports,each of which may allow signals (e.g., R signals and/or signals from/tosector) to be received by or transmitted from DAU 700. In someembodiments, a plurality of physical nodes 710 each includes a Downlinkport 712 and an Uplink port 713. In some embodiments, a physical node710 may also include an additional Uplink port, e.g., to handle adiversity connection. Output ports (e.g., Downlink port 712 and Uplinkport 713) may be coupled to one or more ports (e.g., RE pots) of a basestation. Thus, DAU 700 may be physically coupled to a base station.

Local Router 705 may include one or more second-end ports 740, which maycouple DAU 700 to one or more DRUs of DAUs e.g., via an optical fiber,Ethernet cable, line of sight or non-line of sight microwave connectionetc.). The second-end ports 740 may include LAN or PEER ports.Second-end ports 740 may be configured to send and/or receive signals,such as digital and/or optical signals. In one embodiment at least onesecond-end port 740 couples DAU 700 to another DAU, and at least onesecond-end port 740 couples DAU 700 to a DRU. The local router alsoencodes the signals for transportation over the optical link as well asdecodes the optical signals from the optical link. The Physical Nodesperform the function of translating the RE signals to baseband ortranslating the baseband signals to RE. The DAU can monitor the trafficon the various ports and either route this information to a server orstore this information locally.

FIG. 8 illustrates components of a DRU 800 according to an embodiment ofthe invention. DRU 800 may include a router (i.e., Remote Router 805)DRU may include a network port 810, which may allow DRU 800 to couple(via an Ethernet Switch 815) to a (e.g., wireless) network. Through thenetwork, DRU 800 may then be able to connect to a computer 820. Thus, aremote connection may be established with DRU 800.

Remote Router 805 may be configured by a server, such as server 130,server 725, a server connected to one or more DAUs, and/or any otherserver. Network port 810 may be used as a Wireless access point forconnection to the Internet. The Internet connection may, e.g.,established at the DAU and Internet traffic may be part of the datatransport between the DRUs Physical Nodes and the DAU Physical Nodes.

DRU 800 may include one or more physical nodes 825. Each physical node825 may include one, two or more ports, such as first-end ports 830,each of which may allow for signals (e.g., RF signals and/or signalsfrom mobile devices) to be received by or transmitted from DRU 800. Insome embodiments, a plurality of physical nodes 825 each include one ormore ports configured to send/receive signals (e.g., RE signals) from/toDRU 800. The ports may include, e.g., a Downlink port 827 and an Uplinkport 828 in some embodiments, an additional Uplink port exists forhandling a diversity connection. Physical node ports (e.g., Downlinkoutput port 827 and Uplink output port 828) may be connected to one ormore antennas (e.g., RE antennas), such that signals may be receivedfrom and/or transmitted to, e.g., mobile wireless devices

Remote Router 805 may include one or more second-end ports 835, whichmay couple DRU 800 to one or more DAUs or DRUs. Second-end ports 835 mayinclude LAN or PEER ports, which may (e.g., physically) couple DRU 800to one or more DAUs or DRUs via an optical fiber, Ethernet cable, lineof sight or non-line of sight microwave connection.

It should be appreciated that the specific steps illustrated in FIGS. 5and 6 provide particular methods according to an embodiment of thepresent invention. Other sequences of steps may also be performedaccording to alternative embodiments. For example, alternativeembodiments of the present invention may perform the steps outlinedabove in a different order. Moreover, the individual steps illustratedin FIGS. 5 and 6 may include multiple sub-steps that may be performed invarious sequences as appropriate to the individual step. Furthermore,additional steps may be added or removed depending on the particularapplications. One of ordinary skill in the art would recognize manyvariations, modifications, and alternatives.

Methods shown in FIGS. 5 and 6 or elsewhere described may be performedby a variety of devices or components. For example, some processes maybe performed solely or partly by one or more DAUB. Some processes may beperformed solely or partly by a remote computer, e.g., coupled to one ormore DAUs. Some processes may be performed by one or more DRUs. In someembodiments, shown or described process may be performed by multipledevices or components (e.g., by multiple DAUB, by one DAU and a remoteserver, by one or more DRUs and a DAU, etc.).

Above-described embodiments may be implemented with, distributed basestations, distributed antenna systems, distributed repeaters, remoteradio units, mobile equipment and wireless terminals, portable wirelessdevices, and/or other wireless communication systems such as microwaveand satellite communications. Many variations are possible. For example,embodiments including a single base station may be applied in systemsincluding interconnected base stations. Embodiments may be modified toreplace daisy-chain configurations with star configurations or theconverse or extend daisy-chain configuration into loops. Embodimentsshowing a single server (e.g., connected to a plurality of DAUs) may bemodified to include a plurality of servers (e.g., each connected to adifferent DAU or connected to all DAUs).

FIG. 9 is a high level schematic diagram illustrating a computer system900 including instructions to perform any one or more of themethodologies described herein. One or more of the above-describedcomponents (e.g., DAU 115, DRU 1, server 130, server 725, computer 920,etc.) may include part or all of computer system 900. System 900 mayalso perform all or part of one or more methods described herein. FIG. 9is meant only to provide a generalized illustration of variouscomponents, any or all of which may be utilized as appropriate. FIG. 9,therefore, broadly illustrates how individual system elements may beimplemented in a relatively separated or relatively more integratedmanner.

The computer system 900 is shown comprising hardware elements that canbe electrically coupled via a bus 905 (or may otherwise be incommunication, as appropriate). The hardware elements may include one ormore processors 910, including without limitation one or moregeneral-purpose processors and/or one or more special-purpose processors(such as digital signal processing chips, graphics accelerationprocessors, and/or the like); one or more input devices 915, which caninclude without limitation a mouse, a keyboard and/or the like; and oneor more output devices 920, which can include without limitation adisplay device, a printer and/or the like.

The computer system 900 may further include (and/or be in communicationwith) one or more storage devices 925, which can comprise, withoutlimitation, local and/or network accessible storage, and/or can include,without limitation, a disk drive, a drive array, an optical storagedevice, solid-state storage device such as a random access memory(“RAM”) and/or a read-only memory “ROM”), which can be programmable,flash-updateable and/or the like. Such storage devices may be configuredto implement any appropriate data stores, including without limitation,various file systems, database structures, and/or the like.

The computer system 900 might also include a communications subsystem930, which can include without limitation a modem, a network card(wireless or wired), an optical communication device, an infraredcommunication device, a wireless communication device and/or chipset(such as a Bluetooth device, a WiFi (802.11) device, a WiMax (802.16)device, a zigbee (802.15) device, cellular communication facilities,etc.), and/or the like. The communications subsystem 930 may permit datato be exchanged with a network (such as the network described below, toname one example), other computer systems, and/or any other devicesdescribed herein. In many embodiments, the computer system 900 willfurther comprise a working memory 935, which can include a RAM or ROMdevice, as described above.

The computer system 900 also can comprise software elements, shown asbeing currently located within the working memory 935, including anoperating system 940, device drivers, executable libraries, and/or othercode, such as one or more application programs 945, which may comprisecomputer programs provided by various embodiments, and/or may bedesigned to implement methods, and/or configure systems, provided byother embodiments, as described herein. Merely by way of example, one ormore procedures described with respect to the method(s) discussed abovemight be implemented as code and/or instructions executable by acomputer (and/or a processor within a computer); in an aspect, then,such code and/or instructions can be used to configure and/or adapt ageneral purpose computer (or other device) to perform one or moreoperations in accordance with the described methods.

A set of these instructions and/or code might be stored on acomputer-readable storage medium, such as the storage device(s) 925described above. in some cases, the storage medium might be incorporatedwithin a computer system, such as the system 900. In other embodiments,the storage medium might be separate from a computer system (e.g., aremovable medium, such as a compact disc), and/or provided in aninstallation package, such that the storage medium can be used toprogram, configure and/or adapt a general purpose computer with theinstructions/code stored thereon. These instructions might take the formof executable code, which is executable by the computer system 900and/or might take the form of source and/or installable code, which,upon compilation and/or installation on the computer system 900 (e.g.,using, any of a variety of generally available compilers, installationprograms, compression/decompression utilities, etc.) then takes the formof executable code.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized hardware might also be used, and/or particularelements might be implemented in hardware, software (including portablesoftware, such as applets, etc.), or both. Further, connection to othercomputing devices such as network input/output devices may be employed.

As mentioned above, in one aspect, some embodiments may employ acomputer system (such as the computer system 900) to perform methods inaccordance with various embodiments of the invention. According to a setof embodiments, some or all of the procedures of such methods areperformed by the computer system 900 in response to processor 910executing one or more sequences of one or more instructions (which mighthe incorporated into the operating system 940 and/or other code, such asan application program 945) contained in the working memory 935. Suchinstructions may be read into the working memory 935 from anothercomputer-readable medium, such as one or more of the storage device(s)925. Merely by way of example, execution of the sequences ofinstructions contained in the working memory 935 might cause theprocessor(s) 910 to perform one or more procedures of the methodsdescribed herein.

The terms “machine-readable medium” and “computer-readable medium,” asused herein, refer to any medium that participates in providing datathat causes a machine to operate in a specific fashion. Computerreadable medium and storage medium do not refer to transitorypropagating signals In an embodiment implemented using the computersystem 900, various computer-readable media might be involved inproviding instructions/code to processor(s) 910 for execution and/ormight he used to store such instructions/code. In ninny implementations,a computer-readable medium is a physical and/or tangible storage medium.Such a medium may take the form of a non-volatile media or volatilemedia Non-volatile media include, for example, optical and/or magneticdisks, such as the storage device(s) 925. Volatile media include,without limitation, dynamic memory, such as the working memory 935,

Common forms of physical and/or tangible computer-readable mediainclude, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, or any other magnetic medium, a CD-ROM, any other opticalmedium, punch cards, paper tape, any other physical medium with patternsof holes, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memory chip orcartridge, etc.

Cloud based computing is another example of an embodiment of thecomputer system 900.

The embodiments described herein may be implemented in an operatingenvironment comprising software installed on any programmable device, inhardware, or in a combination of software and hardware. Althoughembodiments have been described with reference to specific exampleembodiments, it will be evident that various modifications and changesmay be made to these embodiments without departing from the broaderspirit and scope of the invention Accordingly, the specification anddrawings are to be regarded in an illustrative rather than a restrictivesense.

Although embodiments of the present invention have, been discussed inrelation to digital DAS networks, the present invention is not limitedto digital implementations and embodiments of the present invention areapplicable to analog DAS networks. In these analog implementations,analog remotes are utilized that receive wireless signals in the uplinkpath and transmit analog signals to an analog host unit. in some analogembodiments, the analog remotes can be connected to the analog host unitusing a star configuration in which the host unit is individuallyconnected to each analog remote using a suitable connection, for examplean analog over fiber connection. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

What is claimed is:
 1. A method for operating a Distributed AntennaSystem (DAS), the method comprising: providing a plurality of DigitalRemote Units (DRUs), each configured to send and receive wireless radiosignals; providing a plurality of inter-connected Digital Access Units(DAUs), each configured to communicate with at least one of theplurality of DRUs via optical signals and each being coupled to at leastone sector of a base station; providing a plurality of sensors operableto detect activity at each of the plurality of DRUs; turning off a DRUdownlink signal at one of the plurality of DRUs in response to an outputfrom one of the plurality of sensors; and turning on a DRU downlinksignal at another of the plurality of DRUs in response to an output fromanother of the plurality of sensors.
 2. The method of claim 1 whereineach of the plurality of DAUs is configured to communicate with the atleast one of the plurality of DRUs by sending and receiving signals overat least one of an optical fiber, an Ethernet cable, microwave line ofsight link, wireless link, or satellite link.
 3. The method of claim 1wherein the plurality of inter-connected DAUs comprises a first DAUconnected to a first sector of the base station and a second DAUconnected to a second sector of the base station.
 4. The method of claim1 wherein each of the plurality of sensors is provided by a signalprocessing processor in each of the plurality of DRUs.
 5. The method ofclaim 1 wherein the plurality of DRUs are connected in a daisy chainconfiguration.
 6. The method of claim 1 wherein the plurality of DRUscomprises a first set of two or more DRUs and a second set of two ormore DRUs, the first set and the second set being coupled to at leastone of the plurality of DAUs in a star configuration.